Coil antennas are used to receive signals at a resonant frequency of a carrier signal. Some coil antennas are tuned to provide a mutual inductance that results in the antenna being excited by the resonant frequency. Some coil antennas are so-called mandrel wound antennas. Mandrel wound antennas are typically manufactured by winding the coils of the antenna on top of each other. Since the relative spacing of the coils in this type of mandrel wound antenna is unpredictable, the mutual inductance of these mandrel wound antennas is unpredictable. These types of mandrel wound antennas are tuned by adjusting the length of the wire while fabricating the antenna.
In contrast to the unpredictable nature of normal mandrel wound antennas, variable pitch antennas are designed with a precise spacing between the coils of the antenna that allow for fine tuning of the mutual inductance between antenna coils. By adjusting the pitch, overall antenna area can be maximized while maintaining the correct total inductance and resonant frequency of the coil.
Coil antennas are commonly used in contactless smart cards. Currently, the majority of variable pitch contactless smart card antennas are manufactured with etched or printed antennas. Etching and printing processes are expensive and entail the use of various materials that are environmentally unfriendly. These disadvantages are addressed by coil antennas manufactured in accordance with the systems and methods described herein.
Some variable pitch smart card antennas using round wire employ ultrasonics to embed the wire into the plastic substrate. These ultrasonic generators are expensive, as are the horns required to transmit the ultrasonic energy into the wire and plastic. In addition, the horns wear down over time and need maintenance or replacement. Further, the ultrasonic embedding process is time consuming and can only be performed on a limited number of plastic materials.